Science help please? (Teaching myself, so no tutors/lecturers/friends to ask). I don't know where the extra H is from :(

My question: where does the H come from to convert NAD+ to NADH, given that it's not lost from the pyruvate?
My current theory is that H bonds to the COCH3 once the CO2 is lost, and that the H is then transferred to NAD+, but figure 9.10 still lists an additional H+ after this occurs. But from where?! I cannot find a succinct answer to this on the internet :(

This is from Campbell Biology (Ninth Edition Australian Version, 2012).
Any help would be greatly appreciated!!!!